Bone pathologies such as osteoporosis (OTP) and osteoarthritis (OA) are rising in incidence with the worldwide rise in life expectancy. The diagnosis is usually obtained using imaging techniques such as densitometry, but with both being multifactorial diseases, several molecular mechanisms remain to be understood. Metabolomics offers the potential to detect global changes which can lead to the identification of biomarkers and a better insight in the progress of the diseases. Our aim was to compare the metabolic profiles of a cohort of 100 postmenopausal women, including subcapital hip fragility fracture patients, women with severe OA of the hip that required the implantation of a hip prosthesis and controls, to find altered metabolites and networks. Nuclear magnetic resonance (NMR) spectroscopy was used to obtain the metabolomic profiles of peripheral blood derived serum, and statistical analysis was performed using MATLAB V.6.5. 30 of the 73 metabolites analysed showed statistically significant differences in a 3-way ANOVA, and 11 of them were present in the comparison between OA and controls after adjustment by covariates, including amino acids, energy metabolism metabolites and phospholipid precursors. PLS-DA analysis shows a good discrimination between controls and fracture subjects with OA patients, and ROC curve analysis demonstrates that control and fracture subjects were accurately discriminated using the metabolome, but not OA. These results point to OA as an intermediate metabolic state between controls and fracture, and suggest that some metabolic shifts that happen after a fracture are also present at weaker intensity in the OA process.

The Interferon-Stimulated Gene 15 (ISG15) has a key role during viral infections, since it can modify and regulate the expression of proteins from the host and from viruses. Isg15 ^−/− mice are more susceptible to infectious diseases. ISG15 is induced by type I Interferons (IFN-I) and apart from defense against pathogens, it can also play an important function in cancer or immune-mediated inflammatory diseases. Previous studies reported that ISG15 expression is increased in post-synaptic dendritic cells (DCs) upon interaction with CD4 + T cells. However, data regarding the role of ISG15 in DCs are scarce. The present study assesses the function of ISG15 in DCs activation, migration and ability to mediate T cell activation using bone marrow-derived DCs (BMDCs) and stimulation with lipopolysaccharide (LPS). Activation of DCs was not impaired but tended to be lower in Isg15 -deficient mice, as observed by reduced CD40 induction in Isg15 ^−/− BMDCs. Isg15 ^−/− BMDCs induced less proliferation and Granzyme B expression in co-cultured CD8 + T cells. Interestingly, Isg15 ^−/− BMDCs secreted reduced levels of the pro-inflammatory cytokines IL-1β and IL-12 upon LPS stimulation. Mechanistically, our data suggest that ISG15 regulates Caspase-1 activity in DCs leading to lower IL-1 β secretion. In conclusion, this study reveals an essential role for ISG15 modulating DCs inflammatory activity and raises new questions regarding the specific mechanisms of how this protein regulates innate immune responses.

Despite the rising incidence of osteoporosis (the most common bone disorder) as life expectancy increases worldwide, the genetic and metabolic factors contributing to this multifactorial disease are still poorly understood. This study investigated the role of arginine metabolism in bone formation and its potential for preventing bone loss in postmenopausal osteoporosis. The osteogenic effects of arginine were evaluated in vitro by determining calcium mineral deposition and the expression of marker genes in the human osteoblastic cell line Saos-2. In vivo analyses were conducted in ovariectomized mice treated with arginine, focusing on femoral bone microarchitecture, marker gene expression and serum metabolite profiles. Arginine treatment enhanced calcium deposition and osteoblastic differentiation in vitro. In contrast, however, this treatment had a deleterious effect in vivo, exacerbating trabecular bone loss. These results are particularly relevant given the wide availability of arginine as a dietary supplement, and our findings underscore the necessity of verifying the safety of nutritional supplements in different populations and in the presence of disease.

Much of the genetic variance associated with osteoporosis is still unknown. Bone mineral density (BMD) is the main predictor of osteoporosis risk, although other anthropometric phenotypes have recently gained importance. The aim of this study was to analyze the association of SNPs in genes involved in osteoblast differentiation and function with BMD, body mass index (BMI), and waist (WC) and hip (HC) circumferences. Four genes that affect osteoblast differentiation and/or function were selected from among the differentially expressed genes in fragility hip fracture (FOXC1, CTNNB1, MEF2C, and EBF2), and an association study of four single-nucleotide polymorphisms (SNPs) was conducted in a cohort of 1001 women. Possible allelic imbalance was also studied for SNP rs87939 of the CTNNB1 gene. We found significant associations of SNP rs87939 of the CTNNB1 gene with LS-sBMD, and of SNP rs1366594 of the MEF2C gene with BMI, after adjustment for confounding variables. The SNP of the MEF2C gene also showed a significant trend to association with FN-sBMD (p = 0.009). A possible allelic imbalance was ruled out as no differences for each allele were detected in CTNNB1 expression in primary osteoblasts obtained from homozygous women. In conclusion, we demonstrated that two SNPs in the MEF2C and CTNNB1 genes, both implicated in osteoblast differentiation and/or function, are associated with BMI and LS-sBMD, respectively.